Extrusion apparatus



Jan. 23, 1968 D. GREEN 3,354,717

EXTRUS ION APPARATUS Filed July 27, 1965 United States Patent 3,364,717 EXTRUSION APPARATUS Derek Green, Lytham Saint Annes, England, assignor to United Kingdom Atomic Energy Authority, London, England Filed July 27, 1965, Ser. No. 475,088 Claims priority, application Great Britain, Aug. 10, 1964, 32,544/ 64 3 Claims. (Cl. 72253) ABSTRACT OF THE DISCLOSURE A hydrostatic extrusion assembly chargeable as a unit into a pressure container, comprising a cylinder having one end open and connecting at its other end with a coextensive extrusion container of smaller internal diameter, the extrusion container being formed from a number of part-annular segments, the extrusion container and the cylinder being contained within a common tubular sheath, the extrusion container being fitted with a die at its end remote from the cylinder, a plunger being entered into the bore of the extrusion container at its other end and the plunger having the head fitting and slidably sealed in the cylinder.

This invention relates to extrusion apparatus and in particular to apparatus for carrying out a hydrostatic extrusion process. In a conventional extrusion process a billet held within a container is subjected to a direct mechanical loading to extrude the billet from the container through a die. The billet is a close fit in the container and extrusion pressure is applied on the end face of the billet by a ram operating in the bore of the container. Hydrostatic extrusion has several advantages over conventional extrusion and differs from conventional extrusion in that a liquid is used to apply extrusion pressure on the billet. The liquid envelops the billet in the container and is pressurized to act directly on the billet. Because the liquid envelops the billet there is no frictional contact between the container and the billet. Die friction is also reduced because the pressurized fluid adjacent the throat of the die provides hydrodynamic lubrication between the extruding material and the die.

The pressure which can be applied in the hydraulic liquid in the container to act on the billet is limited by the resistance of the container to internal pressure. Containers of simple monobloc construction are limited to the containment of pressures of about 50 tons per square inch. Containers of special design can be made to contain pressures of up to 100 tons per square inch but this is about the maximum pressure which can be used Without deforming such containers plastically thus leading to ultimate failure of the containers.

A pressure of 100 tons per square inch is suificient for hydrostatic extrusion of the majority of materials but certain materials such as tool steels require much higher pressures for example 200 tons per square inch and above.

According to the present invention a hydrostatic extrusion assembly chargeable as a unit into a pressure container comprises a cylinder having one end open and connecting at its other end with a coextensive extrusion chamber of smaller internal diameter than the internal diameter of the cylinder, the extrusion chamber being fitted with a plunger, said plunger having a head, of larger cross sectional area than the cross sectional area of the plunger, fitting in the cylinder, an extrusion die being mounted at the end of the extrusion chamber remote from the cylinder, the extrusion chamber comprising a ring formed from a plurality of part annular segments having abutting radial faces, the segments of the extrusion chamber being bound externally by a thin tubular Patented Jan. 23, 1968 sheath which also embraces the cylinder and cojoins it with the extrusion chamber, a thin liner tube being provided in the bore of the extrusion chamber to prevent ingress of hydraulic liquid between the segments of the container at their abutting radial faces and means being provided sealing the end face of the extrusion container remote from the cylinder so as to prevent ingress of hydraulic liquid between the abutting radial faces of the segments of the extrusion chamber at said end face of the extrusion chamber.

In use the extrusion assembly having a billet loaded in the extrusion chamber is charged into a pressure container. The space in the extrusion chamber surrounding the billet and the space in the pressure container surrounding the extrusion assembly are filled with hydraulic liquid. The liquid in the pressure container is pressurized and acts on the head of the plunger in the cylinder of the extrusion assembly so that the plunger is loaded to pressurize the hydraulic liquid in the extrusion chamber surrounding the billet causing extrusion of the billet through the die. As the head of the plunger is of larger area than the cross sectional area of the plunger a higher pressure is generated in the liquid in the extrusion chamber than is applied in the liquid in the pressure container. For example if the area of the plunger head is four times the cross sectional area of the plunger and a pressure of 50 tons per square inch is applied in the hydraulic liquid in the pressure container a pressure of 200 tons per square inch will be generated in the extrusion chamber. In a conventional extrusion chamber of solid construction it is the tensile hoop stresses arising in the chamber which give rise to yield of the material of the container. No tensile hoop stresses can arise in the segments of the container as employed in the assembly of the invention and the pressure of the hydraulic liquid in the pressure container acting on the thin tubular sheath, which embraces the segments of the extrusion chamber, pressurizes the tubular sheath inwards to apply an inwards radial loading on the segments to hold the segments together against the higher pressure of the hydraulic liquid acting in the bore of the extrusion chamber on the billet. As the segments of the extrusion chamber are not subjected to tensile stressing the segments can be made of materials which although weak in tension are of high compressive strength. For example the segments can be made of ceramics such as alumina or tungsten carbide.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a longitudinal cross sectional elevation of an extrusion assembly in accordance with the invention,

FIGURE 2 is a cross section along the line II1I in FlGURE 1.

In FIGURES 1 and 2 there is shown hydrostatic extrusion apparatus comprising a main pressure container 20 fitted with a ram 21 which is slidably sealed in the container 24} by a copper ring 22 and a rubber O-ring 23. The main pressure container 20 contains an extrusion assembly 24 comprising a die base 25, an extrusion chamber 26 and a cylinder 27. The die base 25, the extrusion chamber 26, and the cylinder 27 are cojoined by a tubular sheath 28 made for example of hard drawn copper. The die base 25 is fitted with an extrusion die 29. An extrusion plunger 30 extends from the cylinder 27 into the extrusion chamber 26, the extrusion plunger 30 having a head 31 fitting in the bore of the cylinder 27 and sealed therein by a copper ring 32 and a rubber O- ring 33.

The extrusion chamber 26 comprises six part annular segments 34 having abutting radial faces 35 the segments 34 being assembled within the tubular sheath 28 of the extrusion assembly 24. The segments are for example made of the steel referenced under British Standards as EN25 which is heat treated for strength by heating to 850 C. and quenching in oil followed by tempering by heating to 200 C. and cooling in still air. The segments 34 can alternatively be made from ceramic materials such as alumina or tungsten carbide, as no hoop tensile stresses can exist in the segments 34.

In use of the apparatus shown in FIGURES 1 and 2 the space in the main container 20 surrounding the extrusion assembly 24 and the space in the bore of the extrusion chamber 26 surrounding a billet 36 to be extruded is filled with hydraulic liquid 37. Loading is applied to the ram 21, by a suitable press, to pressurize the hydraulic liquid 37 in the main container 20. The pressure of the hydraulic liquid 37 in the main container 20 acts on the head 31 of the extrusion plunger 30' so that the plunger 30 is loaded to pressurize the hydraulic liquid 37 in the bore of the extrusion chamber 26 surrounding the billet 36. By pressurization of the hydraulic liquid 37 in the extrusion chamber 26 the billet 36 is caused to be extruded through the die 29. If the hydraulic liquid 37 in the main container 20 is raised to a pressure of 50 tons per square inch and the cross sectional area of the plunger head 31 is made four times the cross sectional area of the body of the plunger 30 the hydraulic liquid 37 in the extrusion chamber 26 will be raised to a pressure of 200* tons per square inch. The pressure of 50 tons per square inch generated in the hydraulic liquid 37 in the main container 20 also acts on the outside surface of the sheath 28 of the extrusion assembly 24. Thus the sheath 28 in the region of the extrusion chamber 26 is pressurized radially inwards to hold the segments 34 of the chamber 26 together against the outwards pressure of the hydraulic liquid 37 in the extrusion chamber 25.

The bore of the extrusion chamber 26 is fitted with a thin liner tube 38 to prevent ingress of the hydraulic liquid 37 between the abutting faces of the segments 34.

It will be noted that the die base 25 being joined to the extrusion chamber 26 by the tubular sheath 28 prevents ingress of the hydraulic liquid 37 between the abutting faces of the segments 34 at the end face of the extrusion chamber 26.

I claim: 1

1. A hydrostatic extrusion assembly chargeable as a unit into a presure container comprising a cylinder having one end open and connecting at its other end with a coextensive extrusion chamber of smaller internal diameter than the internal diameter of the cylinder, the extrusion chamber being fitted with a plunger, said plunger having a head, of larger cross sectional area than the cross sectional area of the plunger, fitting in the cylinder, an extrusion die being mounted at the end of the extrusion chamber remote from the cylinder, the extrusion chamber comprising a ring formed from a plurality of part annular segments having abutting radial faces, the segments of the extrusion chamber being bound externally by a thin tubular sheath which also embraces the cylinder and cojoins it with the extrusion chamber, a thin liner tube being provided in the bore of the extrusion chamber to prevent ingress of hydraulic liquid between the segments at their abutting radial faces, and means being provided sealing the end face of the extrusion chamber remote from the cylinder so as to prevent ingress of hydraulic liquid between the abutting radial faces of the segments of the extrusion chamber at said end face of the extrusion chamber.

2. A hydrostatic extrusion assembly as claimed in claim 1 wherein the extrusion die is mounted in a die base abutting the end face of the extrusion chamber remote from the cylinder, the die base being also embraced by the thin tubular sheath which contains the segments of the extrusion chamber, the die base sealing the end face of the extrusion chamber so as to prevent ingress of hydraulic liquid between the abutting radial faces of the segments of the extrusion chamber at the end face of the extrusion chamber.

3. A hydrostatic extrusion assembly as claimed in claim 1 wherein the segments of the extrusion chamber are made of a ceramic material such as alumina or tungsten carbide.

References Cited UNITED STATES PATENTS 1,836,821 12/1931 Singer 72-271 2,283,791 5/1942 Clark 72-272 3,126,096 3/1964 Gerard 72253 CHARLES W. LANHAM, Primary Examiner.

RICHARD J. HE-RBST, Examiner.

K. C. DECKER, Assistant Examiner. 

